General Introduction
As elevator systems have become more sophisticated, for instance having a large number of elevators operating as a group to service a large number of floors, a need developed for determining the manner in which calls for service in either the "up" or "down" direction registered at any of the floor landings of the building are to be answered by the respective elevator cars. The most common form of elevator system group control divides the floors of the building into zones, there being one or several floors in each zone, with approximately the same number of zones as there are cars in the elevator system which can respond to group-controlled service of floor landing calls. However, this approach has had a number of drawbacks.
A more recent innovation, described in the commonly owned U.S. Pat. No. 4,363,381 entitled "Relative System Response Elevator Call Assignments" of Joseph Bittar (issued Dec. 14, 1982), included the provision of an elevator control system in which hall calls are assigned to cars based upon relative system response (RSR) factors, which taken into account instantaneous system operating characteristics in accordance with a desirable scheme of operation. This scheme includes considering a plurality of desirable factors, the assignments being made based upon a relative balance among the factors in making the ultimate selection of a car to answer a hall call. The '381 invention thus provided a capability of assigning calls on a relative basis. rather than on an absolute basis, and, in doing so, used specific, pre-set values for assigning the RSR "bonuses" and "penalties".
In the invention of the subsequent Bittar U.S. Pat. No. 4,815,568 entitled "Weighted Relative System Response Elevator Car Assignment with Variable Bonuses and Penalties" (issued Mar. 28, 1989), the bonuses and penalties are varied, rather than preselected and fixed as in the prior Bittar '381 invention, as functions, for example, of recently past average waiting time and current hall call registration time, which can be used to measure the relatively current intensity of the traffic in the building. An exemplary average time period which can be used for history is five (5) minutes, and a time period of that order is preferred.
The hall calls are assigned to the cars, when they are received, using initial values of the bonuses and penalties to compute the RSR values.
During system operation, the average hall call waiting time for the selected past time period is estimated for hall calls answered during that time period. The hall call registration time of a specified hall call is computed, from the time when the hall call was registered. According to the invention, the penalties and bonuses are selected, so as to give preference to the hall calls that remain registered for a long time, relative to the past selected period's average waiting time of the hall calls.
When the hall call registration time is small compared to the selected time period's average waiting time, the bonuses and penalties for them are increased. When the hall call registration time is large compared to the past selected time period's average wait time, then the call has high priority. Thus, for these situations, the bonuses and penalties are varied by decreasing them.
The above schemes treat all hall calls equally without regard to the number of people waiting behind the hall call. They also treat all cars equally without regard to the current car load, unless the car is fully loaded. It considers only the current car load, but not the expected car load when the car reaches the hall call floor. As a result the car assigned in one cycle is often de-assigned later, because the car later becomes full, and another car is assigned. Often the assigned car does not have adequate capacity.
The invention of the '307 application uses an "artificial intelligence" methodology to, preferably, collect traffic data and predict traffic levels at all floors in a building at all times of the working day based on historic and real time traffic predictions.
This information is then used to predict the number of people waiting behind the hall call, and the number of people expected to be boarding and deboarding at various car stops.
Using this information, the car load when the car reaches the hall call floor is calculated, and the resulting spare capacity estimated. This spare capacity is matched with the predicted number of people waiting at the hall call floor. Any mismatch between predicted spare capacity and the number of people waiting at the hall call then is used to honor or dishonor the car to answer the hall call, using a hall call mismatch penalty.
The dwell times at various floors are computed using the predicted car load and the passenger deboarding and boarding rates. The car stop penalty and the hall stop penalty are varied as functions of these dwell times and the number of people waiting behind the hall call to be assigned, so that, when a large number of people are waiting, a car with fewer "en route" stops is selected.
The stopping of a heavily loaded car to pick up a few people increases service time for a large number of people. Therefore, this is penalized by, for example, using a car load penalty which varies proportionally to the number of people in the car, but at a lower rate as a function of the number of people waiting behind the hall call.
These penalties are included in the RSR value computations. Thus, the resulting RSR value is affected by the car load at the hall call floor, the number of people waiting at the hall call floor and the number of people boarding and deboarding the car at "en route" stops. All of these values are obtained by using "artificial intelligence" based traffic prediction methodology.
The invention of the '307 application thus distributes the car load and car stops equitably, so as to minimize the service time and the waiting time of passengers and improve handling capacity.
Traffic from the lobby is usually highest in the morning in an office building. This is known as the "up-peak" period, the time of day when passengers entering the building at the lobby mostly go to certain floors and when there is little, if any, "inter-floor" traffic (i.e. few hall calls).
During an up-peak period, elevator cars that are at the lobby frequently do not have adequate capacity to handle the traffic volume to the floors to which they will travel. Some other cars may depart the lobby with less than their maximum (full) loads. Under these conditions, car availability, capacity and destinations are not efficiently matched to the immediate needs of the passengers. The passenger waiting time expands, when these loading disparities are present.
In the vast majority of group control elevator systems in use, waiting time expansion is traceable to the condition that the elevator cars respond to car calls from the lobby without regard to the actual number of passengers in the lobby that intend to go to the destination floor. Two cars can serve the same floor, separated only by some dispatching interval (the time allowed to elapse before a car is dispatched). Dispatching this way does not minimize the waiting time in the lobby, because the car load factor (the ratio of actual car load to its maximum load) is not maximized, and the number of stops made before the car returns to the lobby to receive more passengers is not minimized.
In some existing systems, for instance U.S. Pat. No. 4,305,479 to Bittar et al entitled "Variable Elevator Up Peak, Dispatching Interval," assigned to Otis Elevator Company, the dispatching interval from the lobby is regulated. Sometimes, this means that a car, in a temporary dormant condition, may have to wait for other cars to be dispatched from the lobby before receiving passengers who then enter car calls for the car.
In some elevator systems, cars are assigned floors based on car calls that are entered from a central location. U.S. Pat. No. 4,691,808 to Nowak et al entitled "Adaptive Assignment of Elevator Car Calls," assigned to Otis Elevator Company, describes a system in which that takes place, as does Australian Patent 255,218 granted in 1961 to Leo Port. This approach directs the passengers to cars.
In the invention of U.S. Pat. No. 4,804,069 of Bittar and Thangavelu entitled "Contiguous Floor Channeling Elevator Dispatching" (issued Feb. 14, 1989), passengers may only reach a group of contiguous floors by using one car in a group of cars at a specified time. This assignment is made on a cyclical basis.
According to that invention, in a building having a plurality (X) of contiguous floors above or below a main floor, for instance the floors above a lobby, during the "up-peak period" the dispatching sequence follows a scheme by which the floors are arranged in N contiguous sectors (N being an integer less than X). N or more cars are used to serve the sectors, but each sector is assigned (served) at any one time by only one of the cars. The floors in the sector assigned to (served by) a car are displayed on a indicator at the lobby. Once a car responds to the car calls for floors in the sector it is typically returned to the lobby for assignment once again to a sector. Selection of a sector for assignment is made according to a preset sequence. Cars are selected by the sequence of their approach of a committable position for stopping at the lobby. According to one aspect of that invention, sectors are selected according to numerical order, in effect a "round-robin" selection. The assignment is removed if during a cycle car calls to those floors are not entered for that car in a preset time interval. When an assignment is removed, the doors are closed and then reopened when the car is again assigned to the next sector that is selected. The floors in that sector are then displayed on the indicator.
However, the prior attempts to use such channeling to equalize the number of passengers handled by each sector has been done by selecting equal numbers of floors for each sector, which generally assumes that the traffic floor with time on a floor by floor basis is equal, which is not accurate for many building situations.
In contrast, rather than merely assigning an equal number of floors per sector, the invention of U.S. Pat. No. 4,846,311 of Thangavelu entitled "Optimized `Up-Peak` Elevator Channeling System with Predicted Traffic Volume Equalized Sector Assignments" (issued Jul. 11, 1989) established a method of and system for estimating the future traffic flow levels of the various floors for, for example, each five (5) minute interval, and using these traffic predictors to more intelligently assign the floors to more appropriately configured sectors, having possibly varying numbers of floors or even overlapping floors, to optimize the effects of up-peak channeling.
This estimation can be made using traffic levels measured during the past few time intervals on the given day, namely as "real time" predictors, and, when available, traffic levels measured during similar time intervals on previous days, namely "historic" predictors. The estimated traffic is then used to intelligently group floors into sectors, so that each sector ideally has equal traffic volume for each given five (5) minute period of interval.
Such intelligently assigned sectoring reduces passenger queues and the waiting times at the lobby by achieving more accurate uniform loading of the cars of the elevator system. The handling capacity of the elevator system is thus significantly increased.
Thus, by changing the sector configuration with, for example, each five (5) minute interval, by equalizing estimated traffic volume per sector, the time variation of traffic levels of various floors is appropriately served. Then, as a floor has increasing traffic volume, it has better service and often is included in two adjacent sectors.
The invention of the concurrently filed application (OT-999) eliminates the need for one floor to be in more than one sector, as used in the exemplary embodiment of the '311 patent. The invention of the concurrently filed application is based on the principle that the service can be further improved by not requiring all of the sectors to serve an equal traffic volume and by varying the frequency of car assignment to the sectors as a function of the traffic volume served. Such a scheme will provide high frequency service to sectors handling more than average traffic volume resulting in reduced waiting time for a large number of people. For sectors serving much less than the average sector volume, a minimum frequency will be guaranteed, to limit their maximum waiting time to pre-specified limits.
During down-peak, the floors above the lobby are divided into zones, the number of zones being the number of cars in operation minus one. Each zone consists of equal number of contiguous floors. The cars unloading passengers at the lobby are assigned to the zones in a cyclic order. Once the cars leave the lobby, the RSR algorithm assigns the hall calls to the cars so as to minimize the relative system response measure.
Thus, the algorithms selected for up-peak, down-peak and other-than-peak-periods are different. This is because the traffic in the up-peak is mostly from the lobby to the upper floors, while in the down-peak it is mostly from the upper floors to the lobby. At other times there is lobby oriented and lobby generated traffic, as well as inter-floor traffic requiring an effective non-peak period algorithm.
In selecting optimal elevator dispatch strategies for peak periods, namely up-peak, down-peak and noon time, in the most common practice the start of a peak period is assumed to be the time when two cars either leave the lobby with more than a specified load [such, as for example, fifty (50%) percent of capacity] or arrive at the lobby with more than the specified load, within a specified short time interval of a few minutes. So the dispatcher waits for this event to occur to activate the peak dispatch strategies, such as up-peak channeling and down-peak zone based operation. Such a scheme delays the dispatch of empty cars from the upper floors to the lobby during the up-peak period and from the lobby to the upper floors during the down-peak period. This often results in large passenger queues and waiting time at the lobby at the start of the up-peak period and at several upper floors at the start of the down-peak period.
In elevator systems using sector based operation, the formation of sectors for up-peak channeling and zones for down-peak period operation is delayed resulting in poor service at the start of the peak periods.
Similarly the end of the up-peak period is assumed, in the most common practice, to be the time when it is identified that no car leaves the lobby with more than the specified load within the specified interval. The end of the down-peak period is set to the time when no car arrives at the lobby within the specified interval and with more than the specified load. However, this scheme often deactivates the peak period dispatch strategy before it should actually be done. In some cases it delays the switch over to non-peak period dispatching, which can be effectively served by the RSR dispatcher with "artificial intelligence" to vary the bonuses and penalties. This results in poor service to inter-floor and counter-flow traffic.